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Discussion Starter · #21 ·
I'm extremely confident that there's not an air lock. Today, for good measure, I drained about a gallon of coolant and pulled another vacuum with my vacuum fill tool with the heater on to ensure access to the heater core, and slowly filled the system while stopping and pulling additional vacuum. I repeated this process 4 times, and watched all of the hoses go from collapsed under vacuum to filled with coolant. I purposely overfilled the system and then manually suctioned out the approipate amount of coolant from the expansion tank to ensure a proper fill with no air. Afterwards, I brought the engine to temperature and left it idle with the heater on, parked on an extremely steep street with the radiator cap removed to provide any possible air pockets an opportunity to travel up and escape. No changes. I purchased and replaced the radiator cap afterwards for good measure, and again, no changes. I verified the radiator fan operation using AlfaOBD and watched the radiator fan duty cycle increase as coolant temperatures increased while driving, along with physically stopping and checking that the fans were actually running. Both low speed and high speed operations are functioning.

I don't know what else it could be, other than a faulty/plugged oil cooler. I just placed an order for an entirely new oil filter housing with the attached oil cooler, and I will have it in about a week. In the meantime, does anyone else have any other ideas of what can be causing this? This is unbelievable!
 

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Out of curiosity have you pressure tested it hot? Another thing you can do is put a pressure tester on when cold and do a regen to get it hot and watch the pressure rise in the system. If the pressure is to low in the system it could be boiling your coolant.
 

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This sounds like the same exact problem I had with a 2013 dodge dart. It would over heat when it was pushed or shut off then restarted. no one could figure it out. I went for the problem myself and found that when the car got hot there was a hole or a crack in one of the cylinders that would cause this to happen.It would only happen when you would stop the engine then start again, then it would boil out of the tank on the ground. It was putting a pressurized air pocket in the system. God only knows what the pressure was. So Dodge would not admitt to any of this so I went ahead and drained the cooling system, rinsed it really well, vacuumed it and filled it with clean water, put a can of block seal in it under pressure with a radiator pressure tester when it was cold. I kept the pressure at 21lbs untill it reached full operating temp. Then let it cool, all the time keeping 21lbs of pressure on the system until cold. All the heating problems dissapeared and it worked great for many thousands of miles until I traded it in...... Just a suggestion??
 

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When the fans came on could you feel the heat being pulled from the radiator or was the air cold? cool? warm? or hot ?
 

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If the heater doesn't output heat and the radiator isn't hot when its overheating you have an issue with coolant flow.
Validate the above with a IR thermometer. (top rad hose should be inline with the indicated temp before it overheats then not inline with the indicated temp when it overheats)

If the above is true, the flow could be impacted by the one of the following (flow obstruction (air or blockage or engine pressurization) / water pump / thermostat / coolant valve if it exists).
If the engine is injecting air into the system you will be typically be pushing out coolant; I didn't get that you were pushing coolant and your test didn't indicate exhaust in the coolant. (heads can be a bugger to figure out, in BMW land you see a pile of head issues which only manifest as overheating)

Can you validate coolant flow?
With a cold engine, if you start the jeep with the radiator open can you tell when the tstat opens as the engine warms? Basically looking to validate that you have coolant flow when the tstat is open.

My guess is that you don't have enough flow to start, next guess being that flow restricts when it gets hot (unlikely).
 

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Discussion Starter · #28 ·
Are your active grill shutters opening?
My Jeep Grand Cherokee Summit doesn't have active grille shutters.

Did you ever confirm the Jeep Eco definitely does not have a 3 way valve?
It does not have the 3-way valve. I can't find it anywhere on the vehicle where it exists on the RAM's, there's no corresponding part numbers for the Jeep's and it doesn't exist in any of the Jeep cooling system diagrams.

This sounds like the same exact problem I had with a 2013 dodge dart. It would over heat when it was pushed or shut off then restarted. no one could figure it out. I went for the problem myself and found that when the car got hot there was a hole or a crack in one of the cylinders that would cause this to happen.
Sheesh.. I hope that's not the case here!
When the fans came on could you feel the heat being pulled from the radiator or was the air cold? cool? warm? or hot ?
When the engine is HOT and running in the driveway, the air coming off of the radiator when the fan is running is just "warm".

If the heater doesn't output heat and the radiator isn't hot when its overheating you have an issue with coolant flow.
Validate the above with a IR thermometer. (top rad hose should be inline with the indicated temp before it overheats then not inline with the indicated temp when it overheats)

If the above is true, the flow could be impacted by the one of the following (flow obstruction (air or blockage or engine pressurization) / water pump / thermostat / coolant valve if it exists).
If the engine is injecting air into the system you will be typically be pushing out coolant; I didn't get that you were pushing coolant and your test didn't indicate exhaust in the coolant. (heads can be a bugger to figure out, in BMW land you see a pile of head issues which only manifest as overheating)

Can you validate coolant flow?
With a cold engine, if you start the jeep with the radiator open can you tell when the tstat opens as the engine warms? Basically looking to validate that you have coolant flow when the tstat is open.

My guess is that you don't have enough flow to start, next guess being that flow restricts when it gets hot (unlikely).
Out of curiosity have you pressure tested it hot? Another thing you can do is put a pressure tester on when cold and do a regen to get it hot and watch the pressure rise in the system. If the pressure is to low in the system it could be boiling your coolant.
Responding to both of you in this message. There's some excellent ideas here so I went out and purchased a radiator pressure tester that's compatible with the neck on my Jeep Grand Cherokee. I started with a cold engine, and let the pressure build naturally (I didn't pump any pressure into the cooling system). I left it idle for about 15 minutes, and then initiated a manual DPF regeneration cycle with AlfaOBD. The most that the system reached during the regen cycle was 7 psi, and everything was at full operating temps. Using an IR thermometer, during the regen cycle, the upper radiator hose was 173*F and the lower radiator hose was 144*F (about a 30*F differential). Once the regen cycle completed, I left it idle for about 10 minutes, and these two radiator hoses equalized in surface temperatures.

After this 10 minute idle period, I held the RPM at 2000 RPM while stationary on the driveway and after a few minutes, everything got real hot - oil heated to 223*F and coolant heated to 213*F (which is the next step up from the middle on the coolant temp gauge inside the cabin, so clearly starting to overheat just sitting stationary - the Jeep uses an analog gauge). Radiator fans were only running very low. Using the IR thermometer, both the upper and lower radiator hoses were at 196*F, the coolant hose entering the EGR cooler was 194*F, the oil cooler hose was at 122*F, and the radiator fins had a 95-105*F surface temp from the best that I could tell, shooting through the grille. At the end of all this, the most that the cooling system ever reached at the expansion tank was 12 PSI.

So, what does this tell me? Does the oil cooler indeed have an internal blockage considering its hose is around 74*F cooler? Why do the radiator fins have such a low surface temp? Is the hot coolant stopping at the oil cooler and not passing through and making its way to the radiator, thus also being the reason for such high oil temps with no load? Why is the overall system pressure so low? Shouldn't it have reached its full pressure (Around 20 psi? Or am I mistaken?) by the end of all of this?

Thanks again to everyone for their insight. It is truly and genuinely appreciated.
 

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So, what does this tell me? Does the oil cooler indeed have an internal blockage considering its hose is around 74*F cooler? Why do the radiator fins have such a low surface temp? Is the hot coolant stopping at the oil cooler and not passing through and making its way to the radiator, thus also being the reason for such high oil temps with no load?
It will be interesting to see what happens when you change the oil cooler. Maybe try back flushing the old oil cooler to see what comes out of it.
As for the low surface temp of the radiator, if your using an infrared temp gun they are not accurate when sensing in a moving air stream. A bead probe on the fin surface out of the moving airflow will read more accurately
 

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Discussion Starter · #30 ·
It will be interesting to see what happens when you change the oil cooler. Maybe try back flushing the old oil cooler to see what comes out of it.
As for the low surface temp of the radiator, if your using an infrared temp gun they are not accurate when sensing in a moving air stream. A bead probe on the fin surface out of the moving airflow will read more accurately
That makes sense regarding the radiator surface temp and IR temp gun. Unfortunately, the Jeep grille is too small/tight to manually reach and put anything against the radiator. I will definitely back flush the old oil cooler as an experiment. I am receiving the new part on Thursday of next week.

What is your thoughts regarding the 74*F lower temperature of the oil cooler hose versus the other hoses?

Does anyone know the operating PSI of the cooling system - i.e. what PSI that a normally functioning system should naturally reach at full operating temps?
 

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Does anyone know the operating PSI of the cooling system - i.e. what PSI that a normally functioning system should naturally reach at full operating temps?
The pressure cap on the degas bottle is 21 psi and really not an expected pressure while running, but as the coolant expands the pressure of course can rise up to the rated cap pressure. The higher the pressure in the system gets, the boiling point of the coolant goes up also. Unless your towing heavy with +230° coolant you don't want to be near 21psi
 

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Get one of those temperature guns. Test the plumbing and components of the cooling system.

My own suspicion, despite all your hard work and careful analysis, is that the radiator may have blockages due to partial internal collapse.

I had very similar symptoms to you one. Took ages and tons of $$$$ to pin point the issue.
 

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Discussion Starter · #33 ·
Get one of those temperature guns. Test the plumbing and components of the cooling system.

My own suspicion, despite all your hard work and careful analysis, is that the radiator may have blockages due to partial internal collapse.

I had very similar symptoms to you one. Took ages and tons of $$$$ to pin point the issue.
I flushed the radiator both ways with a radiator flush gun connected to both shop air and a garden hose, and flow was extremely good. Wouldn't flow be constricted in this case, if there was an internal issue/blockage?
 

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Your temps and pressures during regen were good. What is confusing is your temp readings vs actual. These thermostats start opening at 208 F and are not fully open tell 228 F. Just going off your analog gauge readings might be the issue, there could be something wrong in the bcm settings or just the gauge itself. Are you getting overheat messages or possible limited speed warnings?
 

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Discussion Starter · #35 ·
Your temps and pressures during regen were good. What is confusing is your temp readings vs actual. These thermostats start opening at 208 F and are not fully open tell 228 F. Just going off your analog gauge readings might be the issue, there could be something wrong in the bcm settings or just the gauge itself. Are you getting overheat messages or possible limited speed warnings?
It's not a malfunctioning gauge and it's actually overheating, unfortunately. When the temperature starts to rise, and if I don't decrease engine load or pull over, the temperature will shoot all the way up to max. When this happens, oil temperatures will increase to 260-270+ if you continue to drive the vehicle, overheat warnings display, speed is limited, etc. I can open the hood at this point and the coolant is severely expanded due to heat and overflowing out of the expansion tank via the overflow tube.
 

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Blown headgasket?
The OP did a running coolant pressure check and tested for combustion gases in the coolant, one of those test should have shown something if head gasket is bad or even a crack in the head.
 

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What service was it at the dealership for? Wondering if they may have left a rag or other debris in the cooling system, if that's what they were working on. Maybe something that's not blocking flow under light load, but moves as the coolant starts flowing.

Have you checked the hoses to make sure you don't have one collapsing, preventing coolant flow?
 

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Discussion Starter · #39 ·
I purchased and installed the new oil cooler and oil filter housing, and unfortunately, there is NO CHANGE. I am at a complete loss as to what is causing this issue.

The issue is easily repeatable and when the engine is at operating temperature, you can go WOT 2-3 times and watch the oil temperature raise to around 230 F. With the heater on, the air is extremely hot indicating full circulation. If you give it another WOT instead of letting it cool down, the oil temperature will raise to around 235 F, and then the coolant temperature will immediately shoot up from the middle all the way to max. It immediately loses heat out of the vents, and the air becomes ice cold, indicating no circulation. The oil temperature will continue to rise to the 270's into a full overheat/limp mode with the coolant maxed out. Letting it cool down for 20 minutes to get the radiator cap off, you can then restart the engine and you'll have circulation again with full heat out of the vents, as if nothing happened. Is it pressure related?

In the past month, I have:
  • Replaced the thermostat
  • Repeated the issue with no thermostat installed
  • 3X flushed the radiator, engine and heater core
  • Installed brand new Mopar OEM water pump
  • Installed brand new Mopar OEM oil cooler/oil filter housing
  • Installed brand new Mopar OEM radiator cap
  • Installed brand new Mopar OEM EGR cooler under warranty approx 3000 miles ago
  • Pressure tested cooling system multiple times, both with pressure and vacuum
  • Refilled with Mopar 68163848AB coolant mixed to 50/50 with a vacuum fill tool each time, to prevent air locks
  • Checked for combustion gasses in the coolant (leaking head gasket or warped head) using UView Combustion Leak Tester
  • Checked for collapsed hoses during active overheating event. All hoses appear normal and feel full.
 

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I know I raised suspicions about hidden internal radiator blockage, and still think that’s possible. But I’m going to ignore that for now.

That 74deg oil temp has me wondering whether the oil cooler hoses have suffered an internal breakdown and are restricting flow Dealer replaced the cooler but not hoses. I don’t think oil coolers are flow directional…
 
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